The present invention relates to a power stone cutter for cutting stone-like materials such as stone, concrete or asphalt using bits such as grinding stones or disk-shaped diamond blades.
A conventional electric-powered stone cutter generally includes an electric motor, a main body for accommodating therein the electric motor, a handle for moving the main body, and a circular bit driven by the motor. One example of such electric-powered stone cutter is described in Japanese Utility Model Application Kokai No. SHO-60-56. In the disclosed device, a support base extends frontwardly from the main body for facilitating support of the entire cutter by positioning a tip end portion of the support base onto a workpiece. A stepped portion is provided in the support base, so that the stepped portion can abut a corner of the workpiece, whereby the entire cutter can be temporarily held at a position.
Another example of the electric-powered stone cutter is described in a Japanese Utility Model Application Kokai No. SHO-61-71415 in which a roller is attached to a front portion of a safety cover which covers the bit for facilitating movement of the cutter over the workpiece.
In the above conventional power stone cutters, the bit is driven into the workpiece a large amount each time the bit is forced into the workpiece. To this effect, the base or the roller is provided for facilitating extension of the bit into the workpiece through the base or roller. In other words, a large infeed amount of the bit can be provided by forcibly placing the stone cutter onto the workpiece by way of the base or the roller and by projecting the bit through the base or roller a large amount. However, to insure that the force of the bit is channeled toward the workpiece, and not consumed in a reactionary movement in the direction away from the workpiece, the operator must expend a great deal of energy pressing the cutter firmly against the workpiece. This puts a large burden on the operator.
To reduce the burden on the operator, the base or roller is omitted from engine-powered stone cutters and the bit is forced into the workpiece only a small amount at a time. The workpiece is cut through by repeatedly passing the stone cutter back and forth across the area of the workpiece to be cut. Since only a small force is required each time the bit is forced into the workpiece, the burden on the operator is reduced. Examples of conventional engine-powered stone cutters are described in Japanese Utility Model Application Kokai Nos. SHO-63-67063 and SHO-63-67064, and a Japanese Patent Application Kokai No. SHO-62-63060.
In the engine-powered stone cutters, a belt is provided for transmitting rotation of the engine to the bit. The belt facilitates increasing or decreasing the RPM of the bit. Fluctuations in the RPM of the bit caused when the belt slips are easily corrected for by increasing or decreasing the RPM of the engine that powers the bit.
However, it is known that there are many problems with engine-powered stone cutters. For example, the gasoline engine is difficult to start at low temperatures. Also, operators risk pseudo-Raynaud's disease (a vibration syndrome occurring in users of engine powered machinery) from the vibration of the engine. Fumes from the gasoline for running the engine have an unpleasant odor. The engine is noisy. Also, the cutter has a relatively large lateral width, the lateral width being in the thickness direction of the bit, due to the power transmission arrangement between an engine output shaft and the belt, i.e., the engine itself has a large lateral width in the reciprocating direction of the piston, and the belt extends in the direction perpendicular to the reciprocating direction, so that resultant lateral width becomes large. Since an operator must hold the handle positioned adjacent to the engine, the operator is distant from the cutting area of the bit. Accordingly, operability of the stone cutter may be degraded, and it may be rather difficult to observe an exact cutting position, so that cutting accurately along an intended cutting line may be degraded.
Japanese Patent Application Kokai No. HEI5-38669 discloses an electric-powered stone cutter whose handle is pivotally movably provided for enhancing operability and holdability. Further, Japanese Utility Model Application Kokoku No. HEI6-1767 discloses an engine-powered stone cutter having a suction hood provided over the bit.